This invention relates to a substrate assembly for a fluorescent or phosphorescent display panel.
A fluorescent or phosphorescent display panel, namely, a luminescent display panel as generally referred to herein, comprises a substrate assembly comprising, in turn, a substrate of an electrically insulating material, a plurality of segmented electrodes on the substrate, masses of a luminescent material on the segmented electrodes, respectively, and a plurality of electroconductive leads for the segmented electrodes also on the substrate. Each segmented electrode is generally formed in an indentation formed in the substrate in a shape corresponding with the luminescent mass disposed therein and on the segmented electrode so as not to protrude outwardly of the general surface of the substrate. The expression "on the substrate" should therefore be understood to mean that the electrodes and luminescent masses do not necessarily protrude from the general substrate surface. Each segmented electrode and the luminescent mass placed thereon form a display electrode. The substrate may comprise a plurality of substrate layers.
It has been the practice to form the segmented electrodes and the electroconductive leads by firing prints on the substrate of silver or silver-palladium paste at about 600.degree. C, particularly when the substrate is made of glass. The segmented electrodes and conductive leads are consequently about ten microns thick. The segmented electrodes thus formed are incapable of making the luminescent masses luminesce to their fullest brightness. A layer of graphite is therefore interposed between each segmented electrode and the luminescent mass as will later be illustrated with reference to one of the figures of the accompanying drawing. The graphite layer, however, does not adhere tenaciously to the underlying segmented electrode. The adhesion is enhanced by addition to the graphite of a glassy adhesive although brightness is somewhat reduced thereby, especially when the adhesive comprises lead glass that is excellent insofar as adhesion is concerned. The graphite layer is further objectionable because it comes off together with the luminescent mass when it is necessary to remove a luminescent mass that is inadvertently wrongly formed on the graphite layer. In addition, the thickness of about ten microns is undersiredly thick when a layer of an insulating material should be deposited on at least portions of the conductive leads.
The segmented electrodes and the conductive leads have alternatively been formed of tungsten or molybdenum by resorting to metallization techniques specifically when the substrate is made of ceramics. During metallization, the tungsten or molybdenum is inevitably activated in a hydrogen atmosphere to be readily contaminated either during storage of the substrates for subsequent use or during manufacture of the display panels. It is therefore necessary to plate the metallized electrodes and leads with gold as will also be described with reference to the above-mentioned one figure.